The present invention relates to a molded product of fiber reinforced composite material and its manufacturing method, and more particularly relates to a molded product having a substantially flat portion and the other portion more complex than the substantially flat portion.
A base material has been used, in which continuous fibers (hereinafter referred to as “long fibers”) are uniformly spread, in order to reinforce a molded sheet product of Fiber Reinforced Plastics (FRP). The molded product of FRP is generally produced with a manufacturing method such as Resin Transfer Molding (RTM) in an autoclave. This manufacturing method has a merit that it can provide a product with high strength. However, it has a demerit that it requires a large amount of man-hours and a skilled worker because it is necessary to stack thin base materials on a mandrel so that they get to fit its contours.
In contrast to the above-mentioned methods, there is a method called Sheet Molding Compound (SMC), which has a merit that it requires neither a large amount of man-hours nor a skilled worker because the method does not include a process for fitting a base material to the mandrel. The method employs a base material, which includes chops of fibers (hereinafter referred to as “short fibers”) cut to a couple of centimeters or spirally continuous fibers able to move freely. A molded product of SMC is cured under pressure and heat in a mandrel apparatus. Japanese Published Patent Application 8-72186 discloses an art related to this method.
The SMC method has a merit that a complicated shape can be relatively easily molded because the fluid base material made of short fibers is used. At the same time, the method has a demerit that it provides lower in-plane stiffness than that of a molded product using a long-fiber base material.
A molded sheet product usually has a reinforcing rib for increasing out-of-plane stiffness or a boss for its attachment to receiving structure. It has been discovered that conventional materials have the following problems.
A long-fiber base material having low fluidity does not allow integral molding of a flat portion with a rib or a boss. In order to overcome this difficulty, it is necessary not only to mold the rib and boss separately from the flat portion but also to attach them to each other with an adhesive. This undesirably requires an additional step of attachment. Although it may be possible to increase the thickness of the flat portion with additional layers of the long-fiber base material instead of the rib so as to increase its out-of-plane stiffness, it inevitably results in a large amount of man-hours because each layer needs to be manually stacked.
Using only a base material made of short fibers such as chops, which allows integral molding of a flat portion with a rib using SMC method, still poses the problem that in-plane stiffness tends to be lower than that of molding of a long-fiber base material.